Hydroforming dies are used to form a cross-sectional profile in tubular parts. Commonly, a tubular part is placed within a die cavity. The die cavity is then filled with fluid and pressurized to expand the tubular part outward against the die into the desired cross-sectional profile.
The hydroforming die cavity is typically filled in a two-stage process. In the first stage fluid, typically water, is inserted into the die cavity at a first pressure level. Once the die cavity has been filled, pressurized fluid at a higher pressurized level is added. The second stage of high pressure fluid is added to finalize forming of the component within the die cavity. Hydraulic pumps are used to provide the pressurized fluid for the hydroforming.
A low pressure high volume pump is typically used to fill the die cavity during the first fluid fill stage. However, the rate at which the hydraulic die can be filled is limited by the capacity of the low pressure pump. For larger parts the overall fill time for the die cavity can slow the hydroform process.
Furthermore, the low pressure pump allows air to enter the die cavity during the first fluid fill stage. The air must then be eliminated or compressed during the second higher pressure fluid fill stage, also adding time to the hydroform process. The larger the part that is being formed in the die and the greater the air pocket, the longer the forming process will take.